用户输入一个正整数a，求1到a之间的偶数之和怎么编程呀 VF

clear
input "请输入一个整数:" to a
s=0
for i= 2 to a step 2
s=s+i
endfor
?s
return

b=0
c=0
a=inputbox("")
m=a
m=int(m)
a=a mod 2
if m=1 then
msgbox("0")
else
if a<>0 then
do
b=b+2
c=b+c
b=int(b)
loop until b>=m-1
msgbox(int(c))
else
do
b=b+2
c=b+c
b=int(b)
loop until b>=m
msgbox(int(c))
end if
end if

vb的

clea
input "整数=" to a
s=0
for i=1 to a
s=s+iif(i/2=int(i/2),i,0)
endfor
?s